Post whisper message asynchronously in tests

I am not 100% percent sure what is happening but it seems that
newMessageFilter is async operation, result of this operation is assumed
to be used in callbacks. All other tests are doing at least 1 io operation
in between creating a filter and posting a message, and it must be enough
for newMessageFilter to complete.

Setting higher GOMAXPROCS allows Otto vm to execute received io requests
immediatly. While lower number of processes may result in events re-ordering.

https://github.com/ethereum/web3.js/blob/develop/lib/web3/methods/shh.js#L39-L41

I tested this change with GOMAXPROCS=1 and it passes consistently.

t/e2e/whisper/whisper_jail_test.go

@@ -1,7 +1,6 @@
 package whisper
 
 import (
-	"runtime"
 	"testing"
 	"time"
 
@@ -66,11 +65,6 @@ func (s *WhisperJailTestSuite) TestJailWhisper() {
 
 	r := s.Require()
 
-	// Increase number of OS threads that can run go code simultaneously.
-	// Some test cases (namely test 3) require a higher number of parallel
-	// go routines to successfully complete without hanging.
-	runtime.GOMAXPROCS(3)
-
 	keyPairID1, err := s.AddKeyPair(TestConfig.Account1.Address, TestConfig.Account1.Password)
 	r.NoError(err)
 
@@ -192,7 +186,8 @@ func (s *WhisperJailTestSuite) TestJailWhisper() {
 					topics: [topic],
 					symKeyID: keyid
 				});
-
+				// creating a filter is an async operation
+				setTimeout(function() {
 				  // post message
 				  var message = {
 					ttl: 10,
@@ -207,6 +202,7 @@ func (s *WhisperJailTestSuite) TestJailWhisper() {
 				  if (!sent) {
 					throw 'message not sent: ' + JSON.stringify(message);
 				  }
+				}, 0)
 			`,
 			true,
 		},